Methods and apparatus to make substantially uniform losses in optical cross connects

ABSTRACT

A method for cross connecting optical signals includes using a common beam steerer to direct a set of optical signals from a set of input ports to a set of output ports. The method further includes adjusting a curvature of the common beam steerer so that paths of the optical signals have substantially the same effective path length.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of U.S. Utilityapplication Ser. No. 11/008,735 filed Dec. 9, 2004 and entitled “Methodsand Apparatus to Make Substantially Uniform Losses in Optical CrossConnects”.

FIELD OF THE INVENTION

The invention pertains to optical cross connects and switches fortelecommunications. More particularly, the invention pertains to suchstructures which can make substantially uniform insertion losses.

BACKGROUND OF THE INVENTION

A variety of optical telecommunication cross connects, or, switches havebeen developed to facilitate switching between a plurality of opticalinputs and a plurality of optical outputs. Some of the known switcheshave been configured as 2D N×M matrix switches. One such configurationis disclosed in U.S. Pat. No. 6,363,182 entitled “Optical Switch forReciprocal Traffic” issued Mar. 26, 2002. In such switches, a twodimensional array of optical deflectors is used to switch signalsbetween input and output ports.

Architectures using known steering structures, for example, at least oneat the input port or the output port, or both produce varying opticalpath lengths. This in turn results in known 3D cross connects exhibitingvarying insertion losses depending on the effective optical path length.Non-uniformity of the insertion losses is a negative in terms of systemdesign and performance.

There continues to be a need for cross connects which exhibitsubstantially constant insertion losses. Preferably, uniformity ofinsertion loss can be achieved without adding substantial manufacturingcomplexity or cost to the respective cross connects or switches.

SUMMARY OF THE INVENTION

An apparatus for cross connecting optical signals includes a first setof ports, in which members of the first set are adapted to receiveand/or transmit optical signals. The apparatus further includes a secondset of ports, in which members of the second set are adapted to receiveand/or transmit optical signals. In addition, the apparatus includes acommon beam steerer having a curved surface. The first and second setsof ports are positioned relative to the common beam steerer so thatpaths of the optical signals transmitted between the members of thefirst and second sets of ports and steered by the common beam steererhave substantially the same effective path length.

A method for cross connecting optical signals includes using a commonbeam steerer to direct a set of optical signals from a set of inputports to a set of output ports. The method further includes adjusting acurvature of the common beam steerer so that paths of the opticalsignals have substantially the same effective path length.

An apparatus for cross connecting optical signals includes first andsecond input ports, first and second output ports, first and second beamsteerers, and a collimator. The first beam steerer is adapted to receivea first optical signal from the first input port and direct the opticalsignal to the first output port. The second beam steerer is adapted toreceive an second optical signal from the second input port and directthe optical signal to the second output port. The collimator is adaptedto collimate the first optical signal so that a path of the firstoptical signal has substantially the same insertion loss as a path thesecond optical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a portion of an optical cross connect,including a two-dimensional array of ports on a plane, having N rows andM columns, and a correspondingly sized array of ports;

FIG. 1B is an end view of a portion of an optical cross connectincluding a two-dimensional array of ports on a curve, having N rows andM columns, and a correspondingly sized array of ports on a curve,according to an exemplary embodiment of the invention;

FIG. 2 is an end view an optical cross connect including an array ofinput/output ports and a curved beam steerer, according to an exemplaryembodiment of the invention;

FIG. 3 is an end view of an optical cross connect including and inputarray, an output array and a curved beam steerer, according to anexemplary embodiment of the invention;

FIG. 4 is an end view of an optical cross connect including an array ofinput/output ports, a curved beam steerer and a reflective beam steerer,according to an exemplary embodiment of the invention;

FIGS. 5A, 5B and 5C illustrate optical cross connects including arraysof input/output ports, one or more curved beam steerers, according toexemplary embodiments of the invention;

FIGS. 6A, 6B and 6C illustrate optical cross connects including arraysof input/output ports, one curved beam steerer and one or morereflective beam steering devices, according to exemplary embodiments ofthe invention;

FIG. 7 is a flow diagram that illustrates the method of adjusting thecurvature of the curved surface of a beam steerer to be used in a crossconnect, according to an exemplary embodiment of the invention; and

FIG. 8 illustrates an optical cross connect including arrays ofinput/output ports, collimators and reflective beam steerers, accordingto an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

While embodiments of this invention can take many different forms,specific embodiments thereof are shown in the drawings and will bedescribed herein in detail with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention and is not intended to limit the invention to thespecific embodiment illustrated.

Beam steering optical cross connects, described below, exhibit improvedperformance by minimizing path length differences between differentpairs of ports configured on a planar input/output array or a planarinput array and separate, output array. Preferably, path lengths betweeninput and output ports will have close to an optimal optical couplingdistance, as would be establishable by those of skill in the art.

In the present instance, planar arrays can employ beam steerers whichare curved, such as curved mirrors or lenses, to reduce path lengthvariations. Such construction takes advantage of the fact that planararrays can be easier to manufacture and more cost effective than curvedarrays.

Variation in path length can be defined as:Variation=(Max−Min)/Average=2(Max−Min)/(Max+Min).

“Max” is the maximum optical path length. “Min” is the minimum opticalpath length for a selected architecture. Variation is thus a function ofthe difference between maximum path length and minimum path length. Byreducing the difference between maximum and minimum path lengths, by forexample reducing the maximum path length or increasing the minimum pathlength, the path lengths can be expected to move closer to the averageor optimal value and can provide substantially uniform insertion losses.

FIG. 1A shows an existing approach, optical cross connect 100, whichhelps to illustrate some of the concepts incorporated in exemplaryembodiments of the invention. Optical cross connect 100 includes anarrays 105 and 110 having M columns and N rows of ports (which canreceive and/or transmit optical signals) and beam steerers 150 and 155.Accordingly, in cross connect 100, an optical signal 160 can enter port115 of array 105 and be steered by beam steerer 150, in order to bedirected to another port 120 of array 120, and exit as optical signal125. Similarly, an optical signal 125 can enter port 120 of array 110,be steered by beam steerer 155, in order to be directed to port 115 ofarray 105, and exit as optical signal 160.

The various optical path lengths of the planar arrangement of FIG. 1Acan be measured as follows. Ports and beam steerers can be positioned tobe confined to a plane, e.g. arranged in a circle or rectangle on aplane. For example, using the X-Y-Z axes designated in FIG. 1A, an inputport and beam steerer can be placed at the coordinates (x, y) of the X-Yplane on which one array resides and an output port and beam steerer canbe placed at the coordinates (x, y) of the X-Y plane on which the otherarray resides. Accordingly, depending upon the placement of an inputport, output port or a beam steerer, the optical path length between aninput port and an output port can vary. The smallest optical path length(for transmitting a signal between an input port and an output port) ismin=z, the distance of a beam of light running perpendicular to both X-Yplanes. FIG. 1A illustrates the smallest optical path length betweenarrays 110 and 105 as the distance between points 130 and 145. Thelongest optical path length is max=sqrt(x²+y²+z²), the distance from thecoordinates (x_(min), y_(min)) on the X-Y plane of one array to thecoordinates (x_(max), y_(max)) of the X-Y plane of the other array. FIG.1A illustrates the longest optical path length between arrays 110 and105 as the distance between points 130 and 135. The median optical pathlength is median=sqrt(z²+(x/2)²+(y/2)²). FIG. 1A illustrates the medianoptical path length between arrays 110 and 105 as the distance betweenpoints 130 and 140. The fractional or percentage variation isvar=(max−min)/(median)=(sqrt(x²+y²+z²)−z)/sqrt(z²+(x/2)²+(y/2)²).

FIG. 1B shows an exemplary embodiment optical cross connect 105 whichfurther illustrates some of the concepts incorporated in other exemplaryembodiments of the invention. It is similar to the arrangement of FIG.1A except that ports 185, 165, 190, 195, 197, 196, 170 and 180 and beamsteerers (not shown) at those ports are arranged on a curve of a sphere.In FIG. 1B, array 155 has M columns (not shown) and N rows of inputand/or output ports. Array 160 has M columns (not shown) and N rows ofinput and/or output ports. Each of the ports of arrays 155 and 160 cantransmit an optical signal to a beam steerer. Accordingly, an opticalsignal 175, entering port 165 of array 155 can be steered by a beamsteerer (not shown) at port 165, to be directed to port 170 of array160, and exit as optical signal 176. Likewise, an optical signal 175entering port 170 of array 160, can be steered by a beam steerer (notshown) at port 170, to be directed to port 165 of array 155, and exit asoptical signal 175.

The various optical path lengths of the planar arrangement of FIG. 1Bcan be measured as follows. Beam steerers and ports can be confined to acurve, e.g. arranged in a circle or rectangle on a sphere. For example,using the X-Y-Z axes designated in FIG. 1B, an input port can be placedat the coordinates (x, y) of the sphere on which one array resides andan output port can be placed at the coordinates (x, y) of the sphere onwhich the other array resides. Accordingly, depending upon the placementof an input and an output port, the optical path length between an inputport and an output port can vary. Z is the distance between the centersof the two spheres. X and y are the maximum distance transverse orperpendicular to z. Compared to the planar arrangement of FIG. 1A, x andy can be smaller than the x and y of FIG. 1A because the curve's surfacearea is greater than the surface area of the curve when projected onto aplane. Additionally, this greater surface area provides the benefit ofpermitting more beam steerers to be placed onto a given region. Thesmallest optical path length is min=z. FIG. 1B illustrates the smallestoptical path length between arrays 160 and 155 as the distance betweenpoints 180 and 195. The longest optical path length ismax=sqrt(z²+x²+y²), the distance from the coordinates (x_(min), y_(min))on the curve of one array to the coordinates (x_(max), y_(max))coordinates of the curve of the other array. FIG. 1B illustrates thelongest optical path length between arrays 160 and 155 as the distancebetween points 180 and 185. The median optical path length isapproximately median=sqrt((z+d)²+(x/2)²+(y/2)²), where d is the distancefrom center of a sphere to outermost part of the sphere's curvedsurface. FIG. 1B illustrates the median optical path length betweenarrays 160 and 155 as the distance between points 180 and 190. Thefractional or percentage variation is var=(max−min)/(median). The minand max values are identical to planar arrangement of FIG. 1A, but themedian is larger because d>0. This implies that curved surfaces canprovide lower path length variation. For an exemplary embodiment havinga spherical surface, d=R−sqrt(R²−(x²+y²)/4), where R is the radius ofcurvature. For an exemplary embodiment having a parabolic surface,d=(x²+y²)/R, where R can dictate the amount of curvature. In exemplaryembodiments of the invention, the curve can be based on R and z and thusR and z can be varied to for example create an optimal surface, causingthe reduction between minimum and maximum optical paths lengths, whichcan result in substantially uniform insertion losses.

FIG. 2 illustrates an exemplary embodiment optical cross connect 200which includes an array 205, having ports (210-1 to 210-N for receivingand/or transmitting optical signals 215-1 to 215-N). Cross connect 200also includes a curved beam steerer 220 such as a curved mirror.Optionally, beam steerers can be used at any of the ports 210-1 to 210-Nto steer one of the optical signal 215-1 to 215-N onto the curved beamsteerer 220. The curvature of beam steerer 220 can be configured by forexample by adjusting R and z to achieve an end result of reducing thedifference between shorter path lengths (for example the path made fromsegments 225 and 235) and longer paths lengths (for example the pathmade from segments 230 and 240). As a result, the variation in insertionlosses between paths of minimum and maximum distances can be reduced.Furthermore, by reflecting signals back to array 205 to exit at one ofthe ports 210-1 to 210-N, curved beam steerer 220 can eliminate the needfor both an input and an output array and eliminate the need for ports210-1 to 210-N to be predefined as inputs or outputs.

FIG. 3 illustrates an exemplary embodiment optical cross connect 300which includes an input array 315 having ports (345-1 to 345-N forreceipt of a plurality of optical signals 320-1 to 320-N), an outputarray 305 having ports (340-1 to 340-N for transmission of a pluralityof signals 310-1 to 310-N). A curved beam steerer 325 (such as a lens)can be positioned between array 305 and array 315. Optionally, beamsteerers can be used at any of the ports 345-1 to 345-N to steer one ofthe optical signals 320-1 to 320-N onto curved beam steerer 325. Thecurvature of beam steerer 325 can be configured for example by adjustingR and z to achieve an end result of reducing the difference betweenshorter path lengths (for example, the length of the path 330) andlonger path lengths (for example, the length of the path made fromsegments 335, 350 and 360), which can make substantially uniforminsertion losses.

FIG. 4 illustrates an exemplary embodiment optical cross connect 400,which includes an array 405, having ports (410-1 to 410-N for receivingand/or transmitting optical signals 415-1 to 415-N). Cross connect 400also includes a curved beam steerer 420 (such as a lens) and a foldingbeam steerer 425 (such as a mirror). Optionally, beam steerers can beused at any of the ports 410-1 to 410-N to steer one of the opticalsignals 415-1 to 415-N onto curved beam steerer 420 and folding beamsteerer 425. In this embodiment, folding beam steerer 425 is planar, buta curved and folding beam steerer may also be used to replace thecombination of curved beam steerer 420 and planar folding beam steerer425 or to just replace planar folding beam steerer 425. The curvature ofbeam steerer 420 can be configured for example by adjusting R and z toachieve an end result of reducing the difference between shorter pathlengths (for example, the length of the path made from segments 430 and440), and longer path lengths (for example, the length of the path madefrom segments 435 and 445), which can make substantially uniforminsertion losses.

FIGS. 5A, 5B and 5C illustrate exemplary embodiment optical crossconnects 500, 530 and 560 respectively which fold light paths using beamsteerers (such as reflective surfaces). Cross connects 500, 530 and 560also illustrate how folding light paths can provided the benefit ofreducing physical system size, in addition to providing substantiallyuniform insertion losses.

FIG. 5A illustrates exemplary embodiment cross connect 500, whichincludes arrays 501 and 504 having ports (502-1 to 502-N and 503-1 to503-N, respectively) for receiving and/or transmitting optical signals(504-1 to 504-N and 505-1 to 505-N, respectively) and curved beamsteerer 507. Optionally, beam steerers can be used at any of the ports502-1 to 502-N and 503-1 to 503-N to steer one of the optical signals504-1 to 504-N and 505-1 to 505-N onto curved beam steerer 507. Thecurvature of beam steerer 507 can be configured for example by adjustingR and z to achieve an end result of reducing path length differences(such as the difference between the path length made from segments 508and 509 and the path length made from segments 510 and 509). Inaddition, arrays 501 and 504 and beam steerer 507 can be positionedrelative to each other to reduce physical system size and reduce thedifference between path lengths.

FIG. 5B illustrates exemplary embodiment cross connect 530, which issimilar to cross connect 500 of FIG. 5A, except that cross connect 530includes two curved beam steerers 537 and 538. Cross connect 530includes arrays 531 and 534, having ports (532-1 to 532-N and 535-1 to535-N, respectively) for receiving and/or transmitting optical signals(533-1 to 533-N and 536-1 to 536-N, respectively). Optionally, beamsteerers can be used at any of the ports 532-1 to 532-N and 535-1 to535-N to steer one of the optical signals 533-1 to 533-N and 536-1 to536-N onto curved beam steerers 537 and 538. The curvature of beamsteerers 537 and 538 can be configured for example by adjusting R and zto achieve and end result of reducing path length differences (such asthe difference in the path length made from segments 539, 540 and 541and the path length made from segments 542, 540 and 541). In addition,arrays 531 and 534 and beam steerers 537 and 538, can be positionedrelative to each other to reduce physical system size and reduce thedifference between path lengths.

FIG. 5C illustrates exemplary embodiment cross connect 560, which issimilar to cross connect 530 of FIG. 5B, except that cross connect 560positions its arrays 561 and 564 and beam steerers 567 and 568differently. Arrays 561 and 564 include ports (562-1 to 562-N and 565-1to 565-N, respectively) for receiving and/or transmitting opticalsignals (563-1 to 563-N and 566-1 to 566-N, respectively). Optionally,beam steerers can be used at any of the ports 562-1 to 562-N and 565-1to 565-N to steer one of the optical signals 563-1 to 563-N and 566-1 to566-N onto curved beam steerers 567 and 568. The curvature of beamsteerers 567 and 568 can be configured for example by adjusting R and zto achieve and end result of reducing path length differences (such asthe difference between the path length made from segments 569, 570 and571 and the path length made from segments 572, 570 and 571). Inaddition, arrays 561 and 564 and beam steerers 567 and 568, can bepositioned relative to each other to reduce physical system size andreduce the difference between path lengths.

FIGS. 6A, 6B and 6C illustrate exemplary embodiment optical crossconnects 600, 630 and 660 which fold light paths using beam steerers(such as mirrors and/or lenses). Cross connects 600, 630 and 660 alsoillustrate how folding light paths can reduce physical system size.Accordingly, configurations similar to cross connects 600, 630 and 660can provide the benefits of reduced physical system size and can makesubstantially uniform insertion losses.

FIG. 6A illustrates exemplary embodiment cross connect 600, whichincludes arrays 601 and 604, having ports (602-1 to 602-N and 605-1 to605-N, respectively) for receiving and/or transmitting optical signals(603-1 to 603-N and 606-1 to 606-N, respectively), beam steerers607-609. Optionally, beam steerers can be used at any of the ports 602-1to 602-N and 605-1 to 605-N to steer one of the optical signals 603-1 to603-N and 606-1 to 606-N onto beam steerers 608 and 609. The curvatureof beam steerer 607 can be configured for example by adjusting R and zto achieve an end result of reducing path length differences (such asthe difference between the path length made from segments 610, 611 and612 and the path length made from segments 610, 611 and 613). Inaddition, arrays 601 and 604 and beam steerers 607-609, can bepositioned relative to each other to reduce physical system size andreduce the difference between path lengths.

FIG. 6B illustrates exemplary embodiment cross connect 630, which issimilar to cross connect 600 of FIG. 6A, except that cross connect 630positions its arrays 631 and 664 and beam steerers 638 and 639differently. Arrays 631 and 634 include ports (632-1 to 632-N and 635-1to 635-N, respectively) for receiving and/or transmitting opticalsignals (633-1 to 633-N and 636-1 to 636-N, respectively). Optionally,beam steerers can be used at any of the ports 632-1 to 632-N and 635-1to 635-N to steer one of the optical signals 633-1 to 633-N and 636-1 to636-N onto beam steerers 638 and 639. The curvature of beam steerer 637can be configured for example by adjusting R and z to achieve and endresult of reducing path length differences (such as the differencebetween the path length made from segments 640, 641 and 642 and the pathlength made from segments 640, 641 and 643). In addition, arrays 631 and634, beam steerers 637-639, can be positioned relative to each other toreduce physical system size and reduce the difference between pathlengths.

FIG. 6C illustrates exemplary embodiment cross connect 660, whichincludes arrays 661 and 664 having ports (662-1 to 662-N and 665-1 to665-N, respectively) for receiving and/or transmitting optical signals(663-1 to 663-N and 666-1 to 666-N, respectively). Cross connect 660also includes a curved beam steerer 667 and a folding beam steerer 668.Optionally, beam steerers can be used at any of the ports 662-1 to 662-Nand 665-1 to 665-N to steer one of the optical signals 663-1 to 663-Nand 666-1 to 666-N onto beam steerers 667 and 668. In this embodiment,folding beam steerer 668 is planar, but a curved and folding beamsteerer may also be used to replace the combination of curved beamsteerer 667 and planar folding beam steerer 668 or to just replaceplanar folding beam steerer 668. The curvature of beam steerer 667 canbe configured for example by adjusting R and z to achieve and end resultof reducing path length differences (such as the difference between thepath length made from segments 669 and 670 and the path length made fromsegments 671 and 670. In addition, arrays 661 and 664, lens 667 and beamsteerer 668, can be positioned relative to each other to reduce physicalsystem size and reduce path length differences.

FIG. 7 is a flow diagram that illustrates an exemplary embodiment methodof adjusting the curvature of the curved surface of a beam steerer toachieve an end result of reducing path length differences and makingsubstantially uniform insertion losses. Some of the steps illustrated inthe flow diagrams may be performed in an order other than that which isdescribed. Also, it should be appreciated that not all of the stepsdescribed in the flow diagram are required to be performed, thatadditional steps may be added, and that some of the illustrated stepsmay be substituted with other steps. At step 710, the effective pathlengths of optical signals (transmitted between input and output portsand steered by a common beam steerer having a curved surface) aremeasured. At step 720, the effective path lengths are checked if theyare substantially the same. If so, the next step is 730, where thecommon beam steerer (having the current curvature of its curved surface)is used to cross-connect the optical signals. Otherwise, the next stepis 740, where R, the radius of the curved surface, is determined. Atstep 750, z, the minimum optical path length of the paths of the opticalsignals (transmitted between the input and output ports and steered bythe common beam steerer) is determined. At step 760, the curvature ofthe common beam steerer is adjusted based on at least one of R and z.The next step is 710.

FIG. 8 illustrates exemplary embodiment cross connect 800, which usescollimators (such as lenses) to make substantially uniform insertionlosses among paths in the cross connect. Cross connect 800 includesarrays 805 and 810, having ports (815-1 to 815-4 and 820-1 to 820-4,respectively) for receiving and/or transmitting optical signals (825-1to 825-4 and 830-1 to 830-4, respectively), collimators (835-1 to 835-4and 840-1 to 840-4, respectively), and reflective beam steerers 845 and850.

Depending up on which ports are used for inputting and outputting asignal, the physical path length of a cross-connected signal may vary.To illustrate this, exemplary cross connections and correspondingphysical path lengths of the optical signals cross connected can bedescribed. An exemplary first cross connection is as follows: opticalsignal 825-4 enters port 815-4, passes through collimator 835-4, strikesreflective beam steerer 845 to be directed to port 820-1 and exit asoptical signal 830-2. For this first cross connection, the physical pathlength is four segments long, passing through the points 855-14, 855-24,855-23, 855-22 and 855-21. An exemplary second cross connect is asfollows: optical signal 825-2 enters port 815-2, passes throughcollimator 835-2, strikes reflective beam steerer 850 to be directed toport 820-3 an exit as signal 830-3. For the second cross connect, thephysical path length is three segments long, passing through the points855-12, 855-22, 855-32 and 855-31.

Due to the physical path length differences of cross connections incross connects such as cross connect 800, variable insertion lossesamong the paths may result. However, collimators (such as 835-1 to 835-4and 840-1 to 840-4) having appropriate focal lengths can be used in thecross connect to make substantially uniform insertion losses among thepaths.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. For example, beam steerers employed by exemplaryembodiments of the present invention, can be focusers, lenses, MEMSdevices, reflectors, mirrors, collimators, acoustic-optical devices,thermo-optical devices, holographic devices, tunable lasers, galliumarsenide waveguides or other waveguides, and/or methods or apparatusthat will transmit an incoming light beam in a desired direction.Moreover, exemplary embodiment port arrays of the present invention,could incorporate beam steerers at each of the ports, input ports,output ports, and input/output ports to unidirectionally and/orbidirectionally transmit light. In addition, exemplary embodiment portarrays can be planar and two-dimensional (having M columns and N rows)or one-dimensional (having N rows) and/or be confined to a spherical ornon-spherical (e.g. parabolic, hyperbolic, elliptical, sine wave) curveand/or where R< >z. Finally, curved beam steerers employed by exemplaryembodiments can have a spherical or non-spherical (e.g. parabolic,hyperbolic, elliptical, sine wave) curvature. It is to be understoodthat no limitation with respect to the specific apparatus illustratedherein is intended or should be inferred. It is, of course, intended tocover by the appended claims all such modifications as fall within thescope of the claims.

1. An apparatus for cross connecting optical signals, comprising: afirst plurality of ports, members of the first plurality of ports areadapted for at least one of receiving, transmitting optical signals; asecond plurality of ports, members of the second plurality of ports areadapted for at least one of receiving, transmitting optical signals; anda common beam steerer having a curved surface, wherein the first andsecond pluralities of ports are positioned relative to the common beamsteerer so that a plurality of paths of optical signals transmittedbetween the members of the first and second pluralities of ports andsteered by the common beam steerer has substantially the same effectivepath length.
 2. The apparatus of claim 1, wherein at least one of thefirst and second pluralities of ports is confined to a plane.
 3. Theapparatus of claim 1, wherein at least one of the first and secondpluralities of ports is confined to a curve.
 4. The apparatus of claim3, wherein the curve is based on at least one of a R and z values. 5.The apparatus of claim 4, wherein R is a radius of the curve.
 6. Theapparatus of claim 4, wherein z is a minimum optical path length of theplurality of paths of optical signals between the members of the firstand second pluralities of ports and steered by the common beam steerer.7. The apparatus of claim 3, wherein the curve is spherical.
 8. Theapparatus of claim 3, wherein the curve is non-spherical.
 9. Theapparatus of claim 3, wherein the curve is parabolic.
 10. The apparatusof claim 4, wherein R<>z.
 11. The apparatus of claim 1, wherein thecommon beam steerer has a reflective surface.
 12. The apparatus of claim1, wherein the common beam steerer is a lens.
 13. The apparatus of claim1, wherein the curved surface is based on at least one of R and zvalues.
 14. The apparatus of claim 13, wherein R is a radius of thecurved surface.
 15. The apparatus of claim 13, wherein z is a minimumoptical path length of the plurality of paths of optical signalstransmitted between the members of the first and second pluralities ofports and steered by the common beam steerer.
 16. An apparatus for crossconnecting optical signals, comprising: a first input port; a secondinput port; a first output port; a second output port; a first beamsteerer, adapted to receive a first optical signal from the first inputport and direct the first optical signal to the first output port; asecond beam steerer, adapted to receive a second optical signal from thesecond input port and direct the second optical signal to the secondoutput port; and a first collimator adapted to collimate the firstoptical signal so that a path of the first optical signal hassubstantially the same insertion loss as a path of the second opticalsignal.
 17. The apparatus of claim 16, further comprising a secondcollimator adapted to collimate the second optical signal so that a pathof the second optical signal has substantially the same insertion lossas a path of the first optical signal.
 18. The apparatus of claim 16,wherein the first collimator is a lens.
 19. The apparatus of claim 17,wherein the second collimator is a lens.
 20. The apparatus of claim 16,wherein the first and second beam steerers have reflective surfaces.